Coated articles and methods for the preparation thereof

ABSTRACT

Glass or plastics substrates which in use are susceptible to misting and which have on at least one surface thereof an antimist coating. The coating is formed from a hydrophilic polymer which comprises a hydrophilic polyurethane which contains from 35 to 60% by weight of water when hydrated and which has a thickness of from 3 μm to 50 μm in its anhydrous state. Substrates in which the coating comprises a first layer formed from a polyurethane which contains from 0 to 35% by weight of water when hydrated and in which a second and subsequent layers are formed from a polyurethane which contains 60 to 90% by weight of water are also described. Methods for forming the coatings are also described.

The present invention relates to an antimist coating for glass orplastics substrates such as polycarbonate substrates which in use aresusceptible to misting and to methods for applying such coatings. Moreparticularly the invention relates to antimist coatings formed fromhydrophilic polyurethanes.

The problem of the misting of automobile, train and aeroplane windows,as well as of lenses used in eye glasses, safety glasses, binoculars andcameras and of safety visors and other transparent surfaces made ofglass or plastics such as polycarbonate is well known. The occurrence ofmisting is particularly dangerous when the substrate involved forms partof a safety device, such as safety goggles, glasses, screens or visorsin which misting of the substrate by moist breath or external watervapour can lead to accidents. There is therefore a requirement for atransparent antimist coating having high light transmission and minimaloptical distortion. Antifogging coatings formed from hydrophilicpolyacrylate polymers and copolymers have been described in for exampleBritish Pat. Nos. 1205767, 1260948 and 1498345, and U.S. Pat. Nos.3,488,215, 3,515,579, 3,520,949 and 3,635,756. However, such coatingshave not been found to be entirely satisfactory through suffering fromone or more of the following disadvantages (a) that when hydrated thecoatings were soft and were therefore susceptible to abrasion andscratching both in use and when being cleaned; (b) that when saturatedthe coating was not sufficiently well adhered to the substrate andreadily delaminated. This was particularly true when the substrate wasglass or a plastics substrate such as polycarbonate, a particularlysevere disadvantage in the case of the latter substrate as polycarbonateis widely used in safety goggles, visors and screens because of its highimpact resistance; (c) the curing temperature required for the coatingprocess involving acrylates is high, usually in excess of 80° C. whichis expensive to operate and requires long heating and cooling periodswhich makes the process of manufacturing slow: (d) when dry and notplasticised by absorbed water, the coatings were relatively brittle andwere susceptible to cracking if flexed.

U.K. Pat. No. 1423269 and U.S. Pat. Nos. 4,018,939 and 3,935,367disclose nonfogging film coatings comprising a block copolymercontaining alternating blocks of polyurethane and hydrophilicpolyacrylate. The copolymer is adhered to the substrate by subjectingthe substrate to a controlled exposure to UV irradiation either beforeor after the nonfogging coating has been cast onto it. The coatings usedin the present invention do not require this extra manufacturing step.

U.S. Pat. No. 4,467,073 and International Patent Application No. WO86/00916 describe an anti-fog liquid coating composition formed bycomplexing or reacting surfactants with hydrophilic polymers which hasbeen cross linked with isocyanate prepolymers. The hydrophilic polymersemployed include polyvinyl-pyrrolidone and copolymers thereof andpolydimethylacrylamide. The patents do not disclose or suggest the useof hydrophilic polyurethanes as is required in the present invention.The patents do not disclose hydrophilic polymers having the watercontent, when hydrated, of the hydrophilic polyurethanes used in thepresent invention. The hydrophilic polyurethanes used in the presentinvention do not contain or require the presence of surfactants to beeffective.

U.S. Pat. Nos. 4,079,160 and 4,435,450 describes abrasion resistantpolyurethane coatings which may be applied to glass or polymericsubstrates. However, antifogging coatings or the use of hydrophilicpolyurethanes is not disclosed or suggested.

U.S. Pat. Nos. 4,156,067 and 4,255,550 describe polyurethane polyetherresins which contain carboxylic acid groups and hydroxyl groups in thepolymer back bone. Such polyurethanes are described as being suitableinter alia as antifog coatings. However, these polymers are described asbeing soluble under alkaline conditions which may preclude their use onsubstrates which are likely to come into contact with alkali that is forexample when the substrate is being cleaned.

U.S. Pat. No. 3,975,350 suggests that cross-linked hydrophilicpolyurethanes may be used as anti-fog coatings but does not disclose thehydrophilic polyurethanes having the water content range required foruse in the present invention. This patent does not disclose the specificsubstrates which are suitable for coating with hydrophilicpolyurethanes.

Surprisingly it has been found that by using a hydrophilic polyurethanewhich will contain from 35 to 60% water when hydrated to form thecoating on a plastics substrate or glass substrate not only is aneffective antimist coating formed which is resistant to spoiling byabrasion, it is also highly adherent to the substrate both when wet andwhen dry. Such coatings are especially effective when used inconjunction with a polycarbonate or polyester substrate. The low curetemperatures required by the use of polyurethane provides a cheaper andquicker manufacturing process.

The hydrophilic polyurethanes for use in the present invention will notbe water soluble, water dispersable or otherwise degraded by water andwill not be affected by aqueous alkaline cleaning solutions such asammonia. Surprisingly the polyurethanes used in the invention are ableto fulfil these criteria without requiring to be copolymerised withother hydrophilic monomers or require special curing processes such asirradiation or cross-linking.

Accordingly the present invention provides a glass substrate which inuse is susceptible to misting which has on at least one surface thereofan antimist coating of a hydrophilic polymer characterised in that thecoating is formed from a hydrophilic polyurethane which contains from 35to 60% by weight of water when hydrated and has a thickness of 3 μm to50 μm in its anhydrous state.

In a second aspect the present invention provides a plastics substratewhich in use is susceptible to misting which has on at least one surfacethereof an antimist coating of a hydrophilic polymer characterised inthat the coating is formed from a hydrophilic polyurethane whichcontains from 35 to 60% by weight of water when hydrated and has athickness of 3 μm to 50 μm in its anhydrous state.

Suitably the thickness of the coating will be from 3 to 50 μm, moresuitably will be from 3.5 to 40 μm and preferably 4 to 20 μm, forexample 6 μm, 8 μm, 10 μm, 15 μm or 20 μm. The thickness of the coatingon the substrate will depend upon the end use to which the substrate isto be put as it is clear that the thicker the coating the more water canbe absorbed and the longer the time will be before the coating issaturated. The thickness given hereinbefore are those which are mostsuitable for most uses, giving a coating of good light transparency andoptical clarity and of satisfactory adhesion to the substrate.

Suitably the hydrophilic polyurethanes used as coatings on the glass orplastics substrates of the invention will be capable of both absorbingand desorbing the water vapour quickly. Favourably the coating whenexposed to water vapour should fog over and clear within 5 seconds atambient temperature, that is about 20° C. The speed with which theantimist property of the coating is manifest varies with the temperatureof the environment in which it operates. It has been found thathydrophilic polyurethanes which contain from 35 to 60% by weight ofwater when hydrated are particularly suitable as coatings in the presentinvention. Most suitably the hydrophilic polyurethane will contain 37.5to 55.0% water when hydrated and preferably 40 to 50%, for example 40%,45% 48% and 50%.

Hydrophilic polyurethanes which may be used as coatings in the presentinvention will be any of those which have the water content ashereinbefore described. The saturation water content of the hydrophilicpolyurethane will not however be such as to cause it to delaminate fromthe substrate. Favoured hydrophilic polyurethanes for use in theinvention are those which are linear, that is are substantially free ofcross-links and which therefore are soluble in organic solvents.

The hydrophilic polyurethanes suitable for use as coatings in thepresent invention may be polyether or polyester polyurethanes. Suitablepolyesters which give rise to polyurethanes include polyesters of adipicacid such as butylene adipate. However it is preferred to usehydrophilic polyurethanes which are polyether polyurethanes. It isparticularly preferred therefore to use hydrophilic polyurethanes whichare linear polyether polyurethanes.

Apt linear polyether polyurethanes may be random polymers containingether units derived from diolic compounds which have been reacted withdiisocyanates. Suitable linear polyether polyurethane include thosedescribed in European Patent Application No. 50035 at page 12 line 1 topage 14 line 10 and at page 32 line 7 to 33 line 12, which areincorporated herein by cross-reference and which have the required watercontent when hydrated.

Particularly apt is a linear polyether polyurethane which employspoly(ethylene glycol) derived blocks alone together with a chainextender and a dissocyanate. Suitably the poly(ethylene glycol) may havea molecular weight of between 600 and 6000 and more suitably of between800 and 2000. A particularly preferred poly(ethylene glycol) has amolecular weight of 1540. Suitably the chain extender will be analiphatic diol or diamine or amineol containing up to 10 carbon atomsand most suitably up to 4 carbon atoms. Suitably the diisocyanate is anaromatic or aliphatic or alicyclic diisocyanate such as toluenediisocyanate, 1,6-hexamethylene diisocyanate or4,4'-dicyclohexyl-methane diisocyanate. A preferred diisocyanate is4,4'-dicyclohexylmethane diisocyanate.

The substrates which are coated by the hydrophilic polyurethanes areplastics materials and glass. Suitable plastics materials includepolycarbonates including 4,4'-isopropylidine diphenol polycarbonate andother polycarbonates described in U.S. Pat. No. 3,305,520 andpoly[diethylene glycol bis(allyl carbonate)], commonly known as CR39(Trade mark), polyesters for example poly(oxy-1,2-ethanediyloxycarbonyl-1,4-phenylene carbonyl) commonly known as Melinex (Trademark) cellulose esters for example cellulose acetate, polymethylmethacrylate, polyamides, for example those which have high impactresistance such as nylon 11. It is also envisaged that substrates ofplastics materials may be coated on one or both surfaces with ahydrophilic polyurethane.

A further special advantage of using an antimist coating of ahydrophilic polyurethane on a polyester material such as Melinex, isthat the combination can be used in place of glass in greenhouses anddouble glazing. In the case of greenhouses it is particularly usefulbecause the glass or uncoated plastics used as glazing in them issusceptible to to condensation which reduces the transmission of actinicradiation through the glazing. By using a coating of hydrophilicpolyurethane the glazing stays clear and as a result means thegreenhouses using the glazing treated in this way may be used moreeffectively even in more northerly latitudes.

The glass substrate may be in the form of tempered glass, plate glass orsafety glass.

When the substrate used is glass, then the adhesion of the hydrophilicpolyurethane to the glass may be improved still further by use of asilane sealant or coupling agent which strengthens the bond between theglass and the polyurethane. Suitable silanes include aminosilanes,mercaptosilanes and epoxysilanes. Preferred are aminosilanes andepoxysilane such as, gammaglycidoxypropyltrimethoxy silane (known asUnion Carbide A-187, Trade mark) and gamma-aminopropyltriethoxy-silane(known as Union Carbide A-1100, Trade mark).

The coupling agent may be applied to the glass surface as a primer coatand the polyurethane applied on top of this coat or preferably it can beincorporated into the polyurethane at 1 to 5% w/w and the two compoundsapplied together.

The special advantages of using an antimist coating of a hydrophilicpolyurethane is (a) its adhesion under both dry and wet conditions, (b)no delamination under application of shear, (c) high resistance offlexural failure, (d) does not affect impact resistance of polycarbonateto which it is applied (e) is tough and resistant to marring and (f) iseffective in temperatures from -40° C. to 100° C. The process ofapplying the coating has the advantages that the polymer is applied as apolymer and is not polymerised and/or cross-linked in situ and that thecoating is `cured` at room temperature leading to cheaper and quickerproduction of coated substrates.

To be usable as an effective antimist coating, the coating must fog overand then clear within 5 seconds, that is the coating must both absorband desorb water quickly. The rate at which absorption and desorptionwill occur is dependent upon temperature.

The coating when in the form of a hydrophilic polyurethane coating doesnot exhibit chromatic aberations, haze or discolouration and does noteffect the light transmission of the substrate to which it is applied.The coating is also unaffected by ultraviolet light, and mild acid andalkali vapours which may be met in an industrial environment.

The coating when in the form of a hydrophilic polyurethane coating ishard enough to resist embedding by small hard particles such as dust andis capable of resisting marring due to the impact caused by droppingonto the surface a metallic ball from up to 6 feet (1.83 meter) away.

The coating when in the form of a hydrophilic polyurethane coating ishard enough to resist abrasion by blunt objects and thus provides ameasure of protection to plastics such as polycarbonates and inparticular poly[diethylene glycol bis(allylcarbonate)] which uncoated issoft and easily scratched.

The coated substrates of this invention may be prepared by conventionalmethods of coating surfaces such as dip coating, spraying, painting,knife-coating, on line coating or by printing. In such processes thehydrophilic polyurethane is dissolved in a suitable organic solvent, forexample as a 1 to 15% solution (by weight) or more aptly as a 4 to 8%solution for dip coating and 1 to 4% for spray coating. Suitable organicsolvents include halogenated hydrocarbons such as methylene dichloride,alkanols such as methanol or ethanol (optionally containing smallamounts of water), ketones such as acetone or methyl ethylketone,2-methoxyethanol or mixtures of these solvents. Preferred solvents areindustrial methylated spirits (IMS) or IMS together with 2methoxyethanol in a ratio of 3:1. Normally and preferably thehydrophilic polyurethane will be applied in its non-hydrated state.

When the coating is to be used in a high quality optical product, suchas on a lens, it is preferred that the coating is applied as the resultof dip coating. In this process the solution of the polymer is placed ina suitable container which is raised mechanically in a controlled mannerto immerse the substrate. The container is then lowered at anappropriate rate to give the desired coating thickness. The thickness ofthe coating depends upon both the solution strength, the viscosity ofthe solution and the rate of withdrawal of the substrate from thecontainer. Favourably the process is carried out at between 15° and 30°C. The solvent is removed from the coating after withdrawal from thesolution using a current of air and preferably a current of warm air ata temperature of 50° to 70° C. Drying at this temperature imparts agloss to the coating thereby presenting a better optical appearance tothe coated substrate.

It is possible, through not preferred, to apply a coating by preformingthe thin film of the hydrophilic polyurethane and adhering it to thesurface of the glass or plastics substrate which is required to berendered antimisting. Aptly, the thin film may be adhered by means of atransparent adhesive which is inert to the film and the substrate.

In a further aspect therefore the present invention provides a processfor forming on at least one surface of plastics substrate an antimistcoating of a hydrophilic polymer comprising adhering to the surface afilm comprising of hydrophilic polyurethane which contains from 35 to60% by weight of water when hydrated and has a thickness of 3 μm to 50μm in its anhydrous state.

In a further aspect therefore the present invention provides a processfor forming on at least one surface of a glass substrate an antimistcoating of a hydrophilic polymer comprising adhering to the surface afilm comprising a hydrophilic polyurethane which contains from 35 to 60%by weight of water when hydrated and has a thickness of 3 μm to 50 μm inits anhydrous state.

In a further aspect therefore the present invention provides a processfor forming on at least one surface of a plastics substrate an antimistcoating of a hydrophilic polyurethane which process comprises immersingthe substrate in a solution of the polyurethane, removing the substratetherefrom at a controlled rate and finally removing the solvent by meansof a current of air to provide the antimist coating of the polyurethane.

In a further aspect therefore the present invention provides a processfor forming on at least one surface of a glass substrate an antimistcoating of a hydrophilic polyurethane which process comprises immersingthe substrate in a solution of the polyurethane, removing the substratetherefrom at a controlled rate and finally removing the solvent by meansof a current of air to provide the antimist coating of the polyurethane.

In an alternative aspect of the present invention the glass or plasticssubstrate may be coated with more than one polyurethane coating in whichthe coating adjacent to the substrate has a lower water content whenhydrated that that of the second or subsequent layers. The advantage forhaving more than one coating is two-fold. Firstly polyurethanes of lowerwater content exhibit greater adherence to the substrate than those ofhigh water content and secondly polyurethanes of high water contentadhere to other polyurethanes more strongly when saturated than they doto the substrate. Thus by using at least two different polyurethanes itis possible to provide a coating which takes up a large amount of waterwhile at the same time does not delaminate from the substrate.

Aptly the polyurethanes are those which have been described hereinbeforeand which have the required water contents and thicknesses. Suitably thepolyurethanes which form the first coating on the substrate will have awater content when hydrated of from 0 to 35% by weight and more suitably10 to 32% and preferably 20 to 30%. Suitably the polyurethane which mayform the second and subsequent coatings will contain when hydrated from60 to 90% by weight of water, more suitably 65 to 85% water, andpreferably 70 to 80% water.

The coatings may be applied in the conventional manner as hereindescribed. The coating of the polyurethane having the lower watercontent when hydrated being first formed on the substrate and then thesecond or subsequent coatings being formed on top of the first.

Accordingly the present invention provides a glass substrate which inuse is susceptible to misting which has on at least one surface thereofan antimist coating of hydrophilic polymer characterised in that thecoating consists of at least two layers the first layer, adjacent to thesubstrate comprising a polyurethane which contains from 0 to 35% byweight of water when hydrated and has a thickness of 3 μm to 50 μm inits anhydrous state and the second and any subsequent layers comprisinga polyurethane which contains from 60 to 90% by weight water whenhydrated and has a thickness of 3 μm to 50 μm in its anhydrous state.

Accordingly the present invention provides a plastics substrate which inuse is susceptible to misting which has on at least one surface thereofan antimist coating of hydrophilic polymer characterised in that thecoating consists of at least two layers the first layer adjacent to thesubstrate comprising a polyurethane which contains from 0 to 35% byweight of water when hydrated and has a thickness of 3 μm to 50 μm inits anhydrous state and the second and any subsequent layers comprisinga polyurethane which contains from 60 to 90% by weight water whenhydrated and has a thickness of 3 μm to 50 μm in its anhydrous state.

DESCRIPTION 1 Preparation of a Hydrophilic Polyurethane

A polyurethane having potential water content of 45% (by weight) whenhydrated was prepared from,

    ______________________________________                                        Polyethylene glycol (Mol. Wt. 1540)                                                               154.0    g (0.1 mole)                                     Ethane diol         18.6     g (0.3 mole)                                     4,4'-dicyclohexylmethane diisocyanate                                                             105      g (0.4 mole)                                     Di-n-butyl tin dilaurate                                                                          0.2%     w/w                                              ______________________________________                                    

The polyethylene glycol and ethane diol were weighed into a breaker andgently warmed to mix the polyethylene glycol and diol. The diisocyanatewas then added and the mixture stirred until a homogeneous solution wasachieved. The catalyst was added and stirring continued for a furtherminute. The mixture was then poured into a high density polypropylenedish and placed in an oven at 90° C. for 2 hours to cure. Thepolyurethane so formed was capable of absorbing water to give a watercontent of 45% when fully hydrate and was soluble in common organicsovents.

Preparation of a Hydrophilic Polyurethane

A polyurethane having a potential water content of 45% (by weight) whenhydrated was prepared from,

    ______________________________________                                        Polyethylene glycol Mol. wt. 1486)                                                                   300.68   g                                             Ethanediamine          24.28    g                                             4,4'-dicyclohexyl methane diisocyanate                                                               175.03   g                                             Di-n-butyl tin dilaurate                                                                             0.2%     (w/w)                                         Methylene dichloride   1125.00  ml                                            Isopropyl alcohol      375.00   ml                                            ______________________________________                                    

Preparation of Hydrophilic Polyurethane

A polyurethane having a potential water content of 65% by weight whenhydrated was prepared from:

    ______________________________________                                        Polyethylene glycol (M W 6000)                                                                    60      g (0.01 mole)                                     Ethanediol          7.44    g (0.12 mole)                                     4,4'dicyclohexylmethane                                                                           33.5    g (0.13 mole)                                     diisocyanate                                                                  Di-n-Butyl tin dilaurate                                                                          0.2%    w/w                                               ______________________________________                                    

Preparation of a Hydrophilic Polyurethane

A polyurethane having a potential water content of 90% by weight whenhydrated was prepared from:

    ______________________________________                                        Polyethylene glycol (M W 8360)                                                                    83.6    g (0.01 mole)                                     Butanediol          0.18    g (0.005 mole)                                    4,4'dicyclohexylmethane                                                                           5.64    g (0.018 mole)                                    diisocyanate                                                                  Di-n-butyl tin dilaurate                                                                          0.2%    w/w                                               ______________________________________                                    

EXAMPLE 1

A solution of a hydrophilic polyurethane (which contains 45% by weightwater when hydrated) was formed by dissolving the polyurethane (600 g)in a solvent (10 liters) comprising a mixture of industrial methylatedspirits (IMS) and 2-methoxyethanol in a ratio of 3:1 by stirring thepolyurethane and solvent together in a glass or polyethylene vessel for24 hours. At the end of this period the solution was filtered to removeany insoluble particles which might impair the finished coating. Thefiltered solution was placed in a clean glass dipping tank mounted onvertically movable platform which was enclosed in a dust freeenvironment.

A substrate in the form of visor formed from polycarbonate was cleanedto remove any grease by immersion in isopropanol and followed byblasting the surface with jets of high pressure air. The dipping processwas carried out in a dust free environment. The visor was attached to aframe above the dipping tank by hooks or suspending clip. The platformon which the dipping tank stood was slowly raised to immerse the visorin the 6% polymer solution. The rate of immersion is controlled and was1 cm/minute in this example. The immersion was stopped before thesolution reached the suspending clip, otherwise unslightly drain markscan be caused on the surface of the visor. When the correct level ofimmersion has been reached, the dipping tank is allowed to descend undercontrolled conditions, for example by using a bleed valve. The rate atwhich the visor is extracted from the tank governs the coatingthickness. Clearly the rate may be varied during the withdrawal processto provide a coating of different thicknesses and to avoid build up ofpolymer at the bottom edge of the visor. In this example the extractionrate was 16 seconds/cm initially, reduced to 30 seconds/cm for the last2 cm.

After extraction from the solution, any remaining drops of solution wereallowed to fall and the visor was then transferred to a warm-air ovenwhen a current of air at 50° C. removed any residual solvent. The dryingprocess takes from 2 to 5 minutes. The visor was further dried on anupward stream of air at ambient temperature for a further 5 minutes. Thecoating formed on both sides of the visor did not show any sign ofcloudiness.

The coating showed good adhesion to the substrate when both wet and dry.The coating was saturated with distilled water and subjected to shear.No break up of the coating was observed.

The antimist properties of the coating was tested by applying moist airto the coated surface and to an uncoated surface and observing the timetaken for the mist to clear in each case. This was carried out at threedifference temperatures 20° C., 0° C. and -25° C. The coated visorcleared at all three temperatures significantly more quickly than theuncoated visor.

The coating upon visual inspection showed no optical aberations.

EXAMPLE 2

A visor is coated on one surface in a similar process to that describedin Example 1 by masking one side of the visor with a prevulcanisedrubber latex. The latex coat is stripped off after the immersion andwithdrawal cycle into the hydrophilic polyurethane solution has beencompleted.

The coating on one surface shows the desired properties of adhesion andantimisting.

EXAMPLE 3

A solution of a hydrophilic polyurethane (which contains 26% by weightof water when hydrated and prepared as described in Example 2 of BritishPatent Application No. 2093190) is formed by dissolving the polyurethane(600 g) in a sovlent (10 liters) comprising a mixture of industrialmethylated spirits and 2-methoxyethanol in a ratio of 3:1. Apolycarbonate visor is then coated using the method described inExample 1. When the first coating is dry a second coating is placed ontop of the first using a solution of a second hydrophilic polyurethane(which contains 85% by weight water when hydrated).

The two-layer coating provides a clear, transparent visor which mayabsorb into its outer layer a large amount of water but which does notbecome detached from the substrate.

EXAMPLE 4

A sheet of polyester, Melinex, was coated on one surface in a similarmanner to that described in Example 2. The polyester sheet may then beused as a glazing panel in a greenhouse whereby the hydrophilicpolyurethane coating faces into the interior of the greenhouse.

EXAMPLE 5

A solution of a hydrophilic polyurethane was formed by the processdescribed in Example 1 except that the solution additionally contained100 g of Union Carbide A-187 (silane coupling agent).

A substrate in the form of a piece of safety glass was cleaned to removeany grease by immersion in isopropanol, followed by blasting the surfacewith jets of high pressure air. The substrate was then coated by theimmersion process described in Example 1.

After the final drying step, the coated glass showed improved antimistproperties compared to uncoated glass. The coating when saturated showedadequate adhesion to the glass.

EXAMPLE 6

A solution of a hydrophilic polyurethane (which contains 26% by weightof water when hydrated and prepared as described in Example 2 of BritishPatent Application No. 2093190) is formed by dissolving the polyurethane(600 g) in a solvent (10 liters) comprising a mixture of industrialmethylated spirits and 2-methoxyethanol in a ratio of 3:1. Apolycarbonate visor is then coated using the method described inExample 1. When the first coating is dry a second coating is placed ontop of the first using a solution of a second hydrophilic polyurethane(which contains 85% by weight water when hydrated).

The two-layer coating provides a clear, transparent visor which mayabsorb into its outer layer a large amount of water but which does notbecome detached from the substrate.

What is claimed is:
 1. A plastics substrate which in use is susceptibleto misting which has on at least one surface thereof an antimist coatingof a hydrophilic polymer in which the coating is formed from ahydrophilic polyurethane which contains from 35 to 60% by weight ofwater when hydrated and has a thickness of 3 μm to 50 μm in itsanhydrous state.
 2. A plastics substrate according to claim 1 in whichthe substrate is a polycarbonate film.
 3. A plastics substrate accordingto claim 1 in which the substrate is a polyester film.
 4. A plasticssubstrate which in use is susceptible to misting which has on at leastone surface thereof an antimist coating of hydrophilic polymer in whichthe coating consists of at least two layers, the first layer adjacent tothe substrate comprising a polyurethane which contains from 0 to 35% byweight of water when hydrated and has a thickness of 3 μm to 50 μm inits anhydrous state and the second and subsequent layers comprising apolyurethane which contains from 60 to 90% by weight water when hydratedand has a thickness of 3 μm to 50 μm in its anhydrous state.